Built-In Resistance Sensor for Measuring Slider Level Pole Width at Point &#34;A&#34; (PWA) for PMR/MAMR Writers

ABSTRACT

A PMR (perpendicular magnetic recording) write head is configured for measurements at the slider level and wafer-level processing stages that will allow a determination of the pole width at a position A (PWA) using the results of a resistance measurement between a main pole (MP) and surrounding write shields (WS) with a layer of conductor in the write gap and a layer of insulating material replacing the side gaps. Knowledge of an accurate value of PWA allows adjustments to be made in the processing of sliders on each rowbar which, in turn improves the capability of delivering the desired statistical variation (sigma) in the distribution of erasure widths for AC signals (EWACS) in a given design which, in turn, gives better overall performance in hard disk drive (HDD) applications.

1. TECHNICAL FIELD

This disclosure relates generally to thin-film perpendicular magnetic writers (PMR) configured for use in conventional perpendicular magnetic recording (PMR) and microwave assisted magnetic recording (MAMR) and particularly to methods of assessing device quality at the wafer level.

2. BACKGROUND

Typically, critical dimension control on the wafer level relies on focused ion beam (FIB) cuts of the devices of interest at some precise locations followed by either scanning electron microscopy (SEM) or transmission electron microscopy (TEM) performed on the sample to obtain dimensional information of interest. This method is destructive and time consuming and limited to a very small sample size for a wafer.

A parameter of great interest is the pole width at the top of the main pole at the expected ABS position after slider lapping, herein denoted “pole width at position A” or PWA. This parameter is directly related to the track pitch capability of the device and also the writability of the device. A better measurement of this parameter on the wafer level and on the row bar level as well would be desirable.

At present, after the wafer is finished, during slider lapping either a magnetic write-width (MWW) meter, a device for measuring the magnetic field profile, or dynamic performance (DP) testing, using a simulated hard disk drive (HDD), is used to obtain the variation pattern of the writer head widths in a row-bar. The information obtained is applied to the processing of subsequent row-bars in order to obtain a better statistical distribution, sigma, (across the row bar) of the erase width produced by an AC signal (EWAC). This is done by bending the row bars according to a pattern determined with the help of the writer resistive lapping guide (WRLG/RLG) sensors which provide a resistance measurement to determine how far lapping has proceeded. Using such methods, a position along the main pole at which to obtain a consistent track width (PWA) can be determined.

MWW meter and DP tester are very time consuming for data collection and also suffer from testing variations. If an electrical measurement can lead to the prediction of PWA of a given device, it could greatly simplify the back-end process.

SUMMARY

It will be an object of the present disclosure to provide a method for determining certain write-head characteristics both on the wafer level and also in the wafer slicing and lapping phase of PMR write head fabrication.

It will be a further object of the present disclosure to provide such a method by use of an additional built-in sensor structure that is fabricated at the same time as the writer resistance lapping guide (WRLG) sensor.

It will be a further object of the present disclosure to provide such a method that can be used to determine PWA for a given device by a resistance measurement at the row level or slider level. This value of PWA can be used as an estimate for other devices.

It will be a further object of the present disclosure to use the information obtained from the new resistance sensor to improve the formation of all the PMR writers in the row bars and to improve the statistical variation (sigma) of the erase width of an AC signal (EWACS).

These advantages are all embodied in the perpendicular magnetic writer (PMR) which may also be configured for microwave assisted magnetic recording (MAMR), that now has a sensor that is disclosed herein as a built-in feature. The built-in sensor is used in conjunction with the WRLG sensor to enable additional information to be determined that would not be determinable using the WRLG sensor alone. It is to be noted that the entire PMR writer, with modifications that are described herein, becomes the sensor by the process of taking a resistance measurement, R, between its main pole (MP) and its write shield (WS) and then evaluating a formula expressing a relationship between R and the quantity PWA that is desired.

As is shown in the air-bearing surface (ABS) view of schematic FIG. 1, this sensor-equipped PMR includes a magnetic main pole (MP) 20 that emerges at the ABS and has a generally trapezoidal ABS face and cross-section that is wider at a trailing-edge surface than at a leading-edge surface. The trailing-edge and leading-edge surfaces are connected by mirror-image symmetrically formed side edge surfaces to complete the trapezoidal cross-section. It is the width of the MP at this position (i.e., position “A”) that it is desired to measure by using an electrical measurement.

A write gap (WG) 10 is formed on the trailing edge of the MP, extending laterally and symmetrically beyond the trailing edge. A trailing shield 40, or write shield, WS, is formed above the write gap. Side gaps (SG) 30 are disposed on either side of the MP and they contact the leading shields 50 disposed to either side of the SG. The WG is filled with a conducting material, such as a stack of Ru/NiCrx/Ru in the PMR case or the microwave generator stack in the MAMR case. The SG 30 are filled with an insulating material such as AlOx. A resistance measuring circuit (not shown) is provided to measure a resistance, R, between the MP and the WS. This will be discussed further below to indicate the relationship between the measured resistance R and the desired value of PWA.

To further clarify the various structures and dimensions to be discussed, we refer now to FIG. 2, which is a side cross-sectional view of the ABS view shown in FIG. 1. The WG 10 is shown formed on the trailing edge of the tapering ABS end of the MP 20. The WS 40 (also called the trailing shield (TS)) is above the WG 10. A leading shield (LS) 50 is formed beneath the MP but separated from it by dielectric material 30. The effective throat height, eTHd, which controls the magnetic flux, is shown measured between the two arrows 70 against the WS 40.

A dielectric layer conformally surrounds the MP and forms a uniform gap between both side edge surfaces of said MP and the leading-edge surface of the MP. This dielectric layer has an upper planar surface that is coplanar with the trailing edge surface of the MP and extends symmetrically away from the MP, forming uniform gaps.

To satisfy these objects, we provide a new sensor that is fabricated at the same time as the WRLG sensor and can provide additional information to augment what is obtained when using only the WRLG sensor. Once this new sensor is calibrated, it can be used to estimate the cross-track pole width (PWA) of a given device at point A. This important information will be obtained by a resistance measurement at the row level or the slider level.

To form this sensor, as shown in FIG. 1, we use a conductive material for the write gap (WG) 10 and insulating material for side gap (SG) 30. After WG material and WRLG material is deposited, they are patterned in the same photo/IBE process to produce a well aligned back-edge for eTHd and WRLGH. Note eTHd is the milled structure between arrows 70 contacting the write gap 10.

During lapping, eTHd (also denoted SH in FIG. 2 although in general eTHd does not equal SH) can be calibrated to WRLG sensor height, then the resistance that is measured between MP 20 and WS 40 can be used to derive PWA for each device, if the MP thickness is not too thin. If the MP thickness is thin, then the resistance will be affected by both PWA and PT.

By forming a writer eTHd structure similarly to what is done in fabricating MAMR heads, then at the same time, we can have the eTHd back edge line up with WRLG sensor back edge. If we electrically isolate the main pole (MP) from the shield structure (WS), with the exception of the leakage produced by the limiting shunting path as explained below, then the resistance from MP to WS that is measured during lapping is a function of eTHd and PWA. Since eTHd can be calibrated to WRLG sensor height, one can derive PWA value for each device during lapping without the need for additional pretest DP measurement or MWW measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic ABS view of a typical slider-mounted PMR writer head with the addition of an element forming a new, built-in, resistance sensor that will enable a determination of writer PWA during wafer processing and during slider processing.

FIG. 2 is a schematic cross-sectional view through the center of the main pole of a portion near the ABS of a typical PMR writer such as that in FIG. 1. We show the SH (distance from ABS to the back edge of the write gap (WG) measured on the WG) and the effective throat height (eTHd) (measured on the trailing shield). In this figure we take SH=eTHd. In practice, the two dimensions may be different.

FIGS. 3, 4 and 5 schematically show the detailed structure of the present slider-mounted PMR incorporated into a HDD. The slider and PMR have been fabricated utilizing the improved methods of the present disclosure.

DETAILED DESCRIPTION

We describe a sensor that is fabricated at the same time as the WRLG sensor and which can provide additional information to augment what is obtained when using only the WRLG sensor. Once this new sensor is calibrated, it is used along with the WRLG sensor (not shown) to estimate the pole width (PWA) of a given PMR device at a point “A”, of its ABS cross-track width. This important information will be obtained by means of an electrical resistance measurement of the resistance between the MP and WS using the sensor at the wafer-level, row level or slider level.

To form this sensor, as shown in the schematic ABS view of a PMR head in FIG. 1 and the side cross-sectional view of the same head in FIG. 2, we will use a conductive material, such as a stack of Ru/NiCrx/Ru, or other conducting material, in the write gap (WG) 10 and use insulating material, such as AlOx for the side gap (SG) 30. The stack can either form a conductive write gap in the case of a PMR writer or it can be the MAMR stack in the MAMR case.

After WG material and WRLG material are deposited they are patterned in the same photo/IBE (photolithographic/ion-beam etch) process used to produce a well-aligned back edge for the WG and WRLG. The horizontal distance from the back edge of the WG 10 to the ABS (see arrows in FIG. 2) is called the SH of the WG.

Depending on the process utilized subsequent to WG SH definition, the effective throat height (eTHd) (70 in FIG. 2), which is the distance from the back edge of the WS to the ABS, can be made to be the same as the WG SH, or to have some offset. If eTHd and SH are different, then the smaller of the two will determine the resistance of the new sensor. For simplicity, we will assume that eTHd and SH are the same (as shown in FIG. 2) in the following discussion.

During lapping, WG SH can be calibrated to the WRLG sensor height so that the resistance that is measured between MP and WS can be used to derive the PWA for each device. If the MP is thin, then the resistance will be affected by both PWA and PT.

If we electrically isolate the main pole (MP) from the write shield structure (WS), with the exception of the leakage produced by the limited shunting path explained below, the resistance from MP to WS that is measured during lapping is a function of SH and PWA. Since SH can be calibrated to the WRLG sensor height, PWA can be derived for each device during lapping without the need for additional dynamic pretest (DP) measurement or MWW measurement.

Referring again to the schematic ABS view of FIG. 1, there is shown an exemplary PMR writer design with the addition of a new conductive element 10 in place of the usual write gap and the modification of other elements so as to create a new electrical resistance sensor that is incorporated into the structure.

Replacing the write gap with a layer of conductive material 10, for example a layer of Ru/NiCrx/Ru, and forming the side gaps 30 with insulating material, we can measure the resistance, R, between the main pole 20 and the write shields 40 and use the result of that measurement to obtain PWA. Using the resistance measurement to obtain PWA requires evaluating the following formula:

R=1/(A+B*PWA*SH+C*SH)+R_L,

In the above formula, R is the resistance measured between the MP 20 and the write shields (WS) 40 and R_L is the resistance of the leads used to make the measurement. Measurements can be made using contact pads or probes. The quantities A, B and C are constants that reflect the contributions to R made by the physical parameters PWA and SH. By arranging a set of measurements using heads in which PWA and SH are varied and measured by other existing means (either SEM or using DP pretest), A, B and C can be obtained. Then, for a wafer-level system in which R is measured and PWA is not known, those values of A, B and C can be used to determine PWA. During lapping the value of SH can be calibrated to WRLG sensor height and then the resistance measured between MP 20 and WS 40 can be used to derive PWA for each device if the MP thickness is not too thin. If the MP thickness is thin, then the resistance R will be affected by both and the calibration formula should also include PT in that case.

Once PWA is determined from the sensor-equipped slider, it's value can be used as an estimate of the value in other sliders to make corrections in their processing. The use of this knowledge will thus provide better consistency in the device structures and an improvement in the statistical distribution (sigma) of the erasure width of an AC signal (EWACS), which was an object of this disclosure.

To form the sensor, a conductive material is needed for the write gap (WG) 10 and an insulating material is needed for the side gap (SG) 20. After WG material and WRLG material are deposited, they are patterned in the same photo/IBE process to produce a well aligned back edge for SH and the WRLG.

The WRLG is based on Ohm's law, R=rho*t*h/L, where rho is the resistivity of the film of material used to make the WRLG, t is the film thickness, L is the length and h is the height, which is reduced as one laps more from the ABS side.

A photo/IBE process is used to produce a well aligned back edge for WG SH and WRLG. During lapping, SH can be calibrated to WRLG sensor height, then the resistance we measure between MP 20 and WS 40 can be used to derive PWA for each device if the MP thickness is not too thin. If the MP thickness is thin, then the resistance will be affected by both PWA and pole thickness (PT) and the PT should be included in the formula.

With the knowledge of both SH (using WRLG height) and PWA (from the value of R) for each device, we can improve EWAC sigma by a more sophisticated bending algorithm. The prior method assumes the neighboring rows had the same EWAC vs. WRLGH relation. The new method will provide a value of an additional parameter, PWA, for better decision making than when only using the results from the WRLG height.

FIG. 3 shows a schematic drawing of a head gimbal assembly (HGA) 1200 that includes a slider-mounted PMR writer 1100, the slider now providing aerodynamic support to the writer when it moves above or below an operational disk recording medium 1140. There is also shown a suspension 1220 that elastically supports the slider-mounted writer 1100. The suspension 1220 has a spring-like load beam 1230 made with a thin, corrosion-free elastic material like stainless steel. A flexure 1230 is provided at a distal end of the load beam and a base-plate 1240 is provided at the proximal end. The slider mounted TAMR writer 1100 is attached to the load beam 1230 at the flexure 1231 which provides the TAMR with the proper amount of freedom of motion. A gimbal part for maintaining the PMR read/write head at a proper level is provided in a portion of the flexure 1231 to which the TAMR 1100 is mounted.

A member to which the HGA 1200 is mounted to arm 1260 is referred to as head arm assembly 1220. The arm 1260 moves the read/write head 1100 in the cross-track direction (arrow) across the medium 1140 (here, a hard disk). One end of the arm 1260 is mounted to the base plate 1240. A coil 1232 to be a part of a voice coil motor (not shown) is mounted to the other end of the arm 1260. A bearing part 1233 is provided to the intermediate portion of the arm 1260. The arm 1260 is rotatably supported by a shaft 1234 mounted to the bearing part 1233. The arm 1260 and the voice coil motor that drives the arm 1260 configure an actuator.

Referring next to FIG. 4 and FIG. 5, there is shown, schematically, a head stack assembly 1250 and a magnetic recording apparatus in which the slider-mounted TAMR writer 1100 is contained. The head stack assembly is an element to which the HGA 1200 is mounted to arms of a carriage having a plurality of arms for engaging with a plurality of disks 1140. The plurality of disks are mounted on a spindle 1261. FIG. 4 is a side view of this assembly and FIG. 5 is a plan view of the entire magnetic recording apparatus.

Finally, the head stack assembly 1250 is shown incorporated into a magnetic recording apparatus 1290. The magnetic recording apparatus 1290 has a plurality of magnetic recording media 1114 mounted on a spindle motor 1261. Each individual recording media 1114 has two TAMR elements 1100 arranged opposite to each other across the magnetic recording media 14 (shown clearly in FIG. 5). The head stack assembly 1250 and the actuator (except for the write head itself) act as a positioning device and support the PMR heads 1100. They also position the PMR heads correctly opposite the media surface in response to electronic signals. The read/write head records information onto the surface of the magnetic media by means of the magnetic pole contained therein.

A member to which the HGA 1200 is mounted to arm 1260 is referred to as head arm assembly 1220. The arm 1260 moves the read/write head 1100 in the cross-track direction (arrow) across the medium 1140 (here, a hard disk). One end of the arm 1260 is mounted to the base plate 1240. A coil 1231 to be a part of a voice coil motor (not shown) is mounted to the other end of the arm 1260. A bearing part 1233 is provided to the intermediate portion of the arm 1260. The arm 1260 is rotatably supported by a shaft 1234 mounted to the bearing part 1233. The arm 1260 and the voice coil motor that drives the arm 1260 configure an actuator.

As is finally understood by a person skilled in the art, the detailed description given above is illustrative of the present disclosure rather than limiting of the present disclosure. Revisions and modifications may be made to methods, materials, structures and dimensions employed in forming and providing a wafer-based process employing a built-in electric sensor for measuring the top pole width, PWA, of a PMR writer that may be configured for MAMR operation while still forming and providing such a structure and its method of formation in accord with the spirit and scope of the present invention as defined by the appended claims. 

1. A method of measuring a pole width at an arbitrary position “A” (PWA) of a trailing edge of an air bearing surface (ABS) of a magnetic pole tip of a specially configured perpendicular magnetic recording (PMR) writer or microwave assisted magnetic recording (MAMR) writer while said PMR or MAMR writer is being processed by a lapping process, said method comprising: providing a wafer comprising a multiplicity of sliders disposed thereon; wherein each of said multiplicity of sliders has a writer resistive lapping guide (WRLG) sensor formed thereon, said sensor being a guide for monitoring the progress of an ongoing lapping process to which said PMR or MAMR writer is being subjected; wherein each said slider comprises a (PMR) or (MAMR) writer formed therein; wherein each said PMR or (MAMR) writer comprises a tapered magnetic pole having a trapezoidal cross-section in an air-bearing surface (ABS) plane wherein said trapezoidal cross-section has a trailing edge and a parallel leading edge and is widest at said trailing edge, having a width there at arm point “A” of said ABS, said width being denoted PWA; wherein each said magnetic pole is surrounded by shields from which it is separated by material-filled gaps of uniform thickness, said gaps comprising a write gap formed between said trailing edge of said magnetic pole and a trailing shield (TS) and laterally disposed mirror symmetric side gaps separating similarly symmetric side edges of said pole from laterally disposed side shields (SS); then, selecting a specially configured slider-mounted PMR or MAMR writer from said multiplicity of sliders in which dielectric material normally filling said write gap of said PMR writer mounted therein has been replaced with a conducting material; and wherein a microwave generating stack fills said write gap of said MAMR writer; and wherein in said specially configured slider, material in said side gaps of said PMR writer having been replaced with insulating material; and forming a resistance measuring circuit on both said specially configured writers to measure a resistance R between said MP and said trailing shield (TS); then, at selected stages of said lapping process, measuring both R and values of said WRLG sensor and obtaining PWA using a formula expressing PWA in terms of said measured values of said WRLG sensor and from said measured value of R.
 2. The method of claim 1 wherein said measured value of R is related to said value of PWA by the following formula: R=1/(A+B*PWA*SH+C*SH)+R_L, where R_L is the resistance of leads used in making said measurement of R and wherein SH is a shield height (thickness) of said TS that is calibrated to said value of WRLG and A, B and C are constants that have been evaluated at selected preliminary steps in said lapping process.
 3. The method of claim 1 wherein said value of PWA obtained from said specially configured PMR or MAMR is used as an estimate of PWA values in PMR or MAMR devices in sliders from said multiplicity of sliders being simultaneously processed by lapping.
 4. The method of claim 2 wherein A, B and C are constants determining the contributions of various elements of said PMR or MAMR writer to said value of R whose values have already been obtained by performing a series of preliminary measurements on said specially configured PMR or MAMR writer prior to reaching states of said lapping process at which values of PWA are required, and within which said preliminary states PWA is actually measured along with R, leaving only A, B and C to be evaluated and to be used thereafter in subsequent measurements.
 5. The method of claim 1 wherein said conducting material is Ru/NiCrx/Ru in said PMR case or a microwave generator stack in said MAMR case.
 6. The method of claim 3 wherein by using said value of PWA as an estimated value of PWA in sliders of adjacent rowbars (parallel slices along a wafer), bending algorithms can be applied in further processing to improve the values of PWA and, thereby, improve the statistical variance, sigma, of the erasure width of an AC signal (EWACS) of sliders to be obtained from said adjacent rowbars.
 7. A built-in sensor for use during processing of slider-mounted PMR (perpendicular magnetic recording) or MAMR (microwave assisted magnetic recording) writers, comprising: a slider selected from a multiplicity of sliders disposed along parallel slices in a wafer wherein each said slider comprises a perpendicular magnetic recording (PMR) writer further comprising a main magnetic pole (MP) having a trapezoidal cross-section in an air-bearing surface (ABS) plane, a write-gap (WG) formed on a trailing edge surface of said MP and extending laterally and symmetrically beyond said trailing edge surface, a trailing shield (TS) above said (WG), side gaps (SG) disposed against and contacting both lateral sides of said MP and side shields (SS) disposed on either side of said SG, wherein said WG is filled with a conducting material; and wherein said SG are filled with an insulating material; and wherein a resistance measuring circuit is provided to measure a resistance between said MP and said TS; whereby a measurement of said resistance during a lapping process on said PMR or MAMR writer is used to determine a width of a trailing edge, PWA, of said MP in said ABS plane.
 8. The built-in sensor of claim 7 wherein said write head comprises a Writer Resistive Lapping Guide (WRLG) sensor for determining lapping depth during a lapping process.
 9. The built-in sensor of claim 8 wherein a resistance R measured using said resistance measuring circuit is used to determine the width of said trailing edge of said MP at a point A (PWA) of said trailing edge when R is measured, by application of the following formula: R=1/(A+B*PWA*SH+C*SH)+R_L, where R_L is the resistance of leads used in making the measurement of R, A, B and C are constants determined empirically by prior simultaneous measurements of R and PWA and SH is the thickness of the TS that is measured using said WRLG.
 10. The built-in sensor of claim 7 wherein said conducting material in said WG is Ru/NiCrx/Ru or other conducting metals, alloys and multilayers.
 11. The built-in sensor of claim 8 wherein said WRLG sensor is a variable resistance sensor, comprising a resistive film whose film thickness, t, determines its resistance according to Ohm's law as expressed by the formula R_(WLG)=rho*t*h/L, where rho is the resistivity of said film, t is said film thickness, h is said film height and L is said film length and wherein, said WRLG sensor is configured so that said film thickness is reduced as the ABS side of a wafer is lapped away and wherein the amount of reduction is established by a measurement of its resistance.
 12. A slider-mounted perpendicular magnetic recording (PMR) writer or microwave assisted magnetic recording (MAMR) writer, comprising: a magnetic main pole (MP) emerging at an air-bearing surface (ABS), said MP having a trapezoidal ABS face that is wider at a cross-track trailing edge surface, denoted “_A_”, said width at “_A_” being denoted PWA, than at a parallel leading edge surface and wherein said trailing and leading edge surfaces are connected by symmetrically formed side edge surfaces; a write gap layer formed over said “_A_” surface and extending symmetrically beyond lateral edges of said “_A_” surface; wherein said write gap layer includes a microwave generating stack in said MAMR writer; side gap layers formed against side edge surfaces, said side gap layers abutting undersides of said write gap layer; wherein the value of PWA has been accurately estimated by means of a built-in electrical resistive sensor measurement taken using a corresponding neighboring slider-mounted PMR writer or a corresponding neighboring slider-mounted MAMR writer having a built-in sensor configured to produce such a measurement, whereby statistical variations in writer parameters are improved and the Erasure Width of an AC signal (EWAC) variance of said PMR writers or said MAMR writers is known within narrower limits.
 13. A head gimbal assembly, comprising the slider-mounted perpendicular magnetic recording (PMR) or microwave assisted (MAMR) writer of claim 12; a suspension that elastically supports said slider-mounted PMR writer or said MAMR writer, wherein said suspension has a flexure to which said slider-mounted PMR writer or said MAMR writer is joined, a load beam with one end connected to said flexure and a base plate connected to the other end of said load beam.
 14. A HDD (Hard Disk Drive), comprising: said head gimbal assembly of claim 13; a magnetic recording medium positioned opposite to said slider-mounted PMR writer or said slider-mounted MAMR writer; a spindle motor that rotates and drives said magnetic recording medium; a device that supports the slider and positions said slider relative to said magnetic recording medium.
 15. The built-in slider sensor of claim 9 wherein said constants A, B and C are treated as variables and determined by a series of at least three independent measurements at selected stopping positions in the lapping process, at which positions R, SH and PWA are simultaneously measured by appropriate measuring devices, whereby A, B and C are simultaneously solved numerically in terms of R, SH and PWA. 